Swedish pop sensation Robyn has lent her singing skills to troubled star Britney Spears - by performing backing vocals on her new single. The With Every Heartbeat star vehemently denied she was writing for Spears in August this year (07), but admitted the singer had recorded some tunes she had already written, including Piece Of Me. She said, "It is not true that I will be writing for Britney. She has recorded some of my songs but they won't be released."